A tumor in the central nervous system (CNS), commonly referred to as a brain tumor, is a mass of abnormal cells located in or next to the brain or spinal cord. A primary brain tumor is one that begins in brain tissue. A metastatic brain tumor has spread to the brain from another part of the body.
Some primary brain tumors include gliomas or meningiomas, and their name depends on their location within or around the brain and CNS, as well as the types of cells from which they develop.
The CNS comprises the brain and spinal cord and controls our personality, senses and basic body functions. The brain can be divided into lobes, each with specific functions (see Brain Anatomy figure below). The two frontal lobes, located behind the forehead, control motor function, problem solving and judgment. Just behind the frontal lobes are the two parietal lobes, which are the primary sensory areas that allow you to touch and feel, as well as control handwriting and body position. Underneath the frontal and parietal lobes are the two temporal lobes, which are responsible for memory and hearing. The two occipital lobes process visual images from your eyes.
A benign (noncancerous) tumor typically does not contain cancer cells. A brain tumor is considered benign when it’s slow-growing, when its cells appear mostly normal under a microscope, and when it has distinct borders, meaning it’s less likely to spread into surrounding tissues. A benign brain tumor is often treated with surgery alone or observed carefully over time. However, a mass of noncancerous cells can be just as dangerous or life-threatening as a malignant (cancerous) tumor if it is in or near an area of the brain that controls crucial functions or near vital vascular structures.
A malignant brain tumor contains cancer cells, grows rapidly and is invasive. The tumor may have roots that extend into surrounding tissue, making the tumor borders less defined and more difficult to remove surgically. Some primary malignant brain tumors may be referred to as “brain cancer” even though they do not fit the typical definition of cancer. Although they may spread to other areas of the brain or spine through the cerebrospinal fluid, brain tumors rarely spread beyond the CNS to distant organs.
Types of brain tumors
The most common primary brain cancers are tumors known as gliomas, which originate in glial cells in the brain and spinal cord. Glial cells surround nerve cells and keep them in place.
The gliomas include astrocytomas arising in star-shaped glial cells called astrocytes, brain-stem gliomas occurring in the lowest part of the brain, ependymomas arising from cells that line parts of the spinal cord, and oligodendrogliomas arising from cells in the brain that make fatty substances that protect nerves.
Other types of brain cancers originate elsewhere in the brain. The most common ones are medulloblastomas arising in the part of the brain called the cerebellum, meningiomas arising in the meninges (the membranes covering the brain), schwannomas arising from cells that line the nerve that controls balance and hearing (Schwann cells), craniopharyngiomas occurring at the base of the brain, germ-cell tumors arising from cells in the brain known as germ cells, and pineal region tumors arising in or near a gland in the brain known as the pineal gland.
Gioblastomas (GBM) are tumors that are believed to arise from astrocytes, the star-shaped cells that make up the supportive tissue of the brain. But some evidence suggests they arise from stem cells within the brain. GBMs usually contain a mix of cell types along with cystic mineral, calcium deposits, blood vessels or a mixed grade of cells. This tumor represents about 15 percent of all primary brain tumors. They increase in frequency with age and affect more men than women.
Although GBMs can be found anywhere in the brain or spinal cord, they are generally found in the cerebral hemispheres of the brain. The most common symptoms are usually caused by increased pressure in the brain and can include headache, nausea, vomiting and drowsiness. Depending on the tumor’s location, other symptoms can include weakness on one side of the body, memory and/or speech difficulties and visual changes.
GBMs are usually highly malignant (cancerous) because the cells reproduce quickly and migrate into the brain substance, and they are supported by a large network of blood vessels. These cells are able to easily invade and live within normal brain tissue. However, they rarely spread elsewhere in the body.
GBMs contain many different types of cells, which is why treatment may include a combination of several approaches. Surgery is typically done first to safely remove as much tumor as possible and relieve pressure on the brain. GBMs have finger-like tentacles and are difficult to completely remove, particularly when they are near parts of the brain that control functions such as language and coordination. Radiation and chemotherapy may be used to slow the growth of tumors that cannot be removed with surgery.
Optune, another treatment option, is a portable, non-invasive device that delivers low-intensity, intermediate frequency, alternating electric fields — referred to as tumor treating fields — that prevent cancer cells from reproducing and cause cancer cells to die. When this device is used, the head is shaved and four sets of electrodes are placed on the scalp. The electrodes are attached to a battery pack and are worn for most of the day. Side effects of the device tend to be minor and can include skin irritation at the electrode sites and a slightly increased risk of headaches and seizures.